Is Wood Ash Good for Grass? How to Use it as Lawn Fertilizer

Wood ash works well as a fertilizer if your lawn doesn’t have any nitrogen deficiency issues. It contains important macronutrients and micronutrients like potassium, phosphorus, calcium, and manganese. To effectively use fireplace wood ash as lawn fertilizer, consider various precautions like gentle application and proper preparation of the lawn soil.

Is fireplace ash good for lawns?

Fireplace ash is good for lawns due to the beneficial properties it offers to the soil and turfgrass. Ash improves soil quality by correcting the pH, while also delivering essential nutrients that boost the health of the grass. However, to avoid grass burn, apply wood ash in the correct form or quantity.

Take note, too, that different types of wood ash carry different amounts of beneficial nutrients and minerals. Hardwood ash (like hickory and oak ash) contains five times more nutrients per cord than softwood ash (like fir and pine ash).

Is Wood Ash Good for Grass?

Can wood ash kill grass?

Improper application of wood grass can kill your turfgrass. Since it’s highly alkaline, fireplace ash will kill grass if it’s added to a lawn where the soil is already alkaline (pH above 7.0). That’s because the ash makes the soil even more alkaline than it originally was.

However, if fireplace wood ash is added to acidic soil where the pH is below 6.0, there should be no negative effects on the grass. That’s because the ash raises the alkalinity to neutral or thereabouts (pH of 7.0- 7.5). This pH range is, in fact, perfect for healthy turf growth and development.

Pro tip: The component that makes wood ash alkaline is the macronutrient calcium, whose quantity in ash varies based on the type of wood used for the fireplace. Due to calcium, the pH of wood ash is usually at 9.0 or more.

Benefits of Wood Ash for Lawns

The advantages of using wood ash on lawns cannot be overstated. By applying ash on your turf you’ll be able to improve the soil quality, boost root development, and boost grass growth, development, and health.

Improves Soil Quality

Turfgrass grows vigorously, stays healthy, and becomes more resistant to drought and other environmental stressors when grown in slightly acidic-neutral soil of 6.5- 7.0 pH. However, when the soil is too acidic, the grass becomes stressed and normal growth is affected.

One of the main factors that lower soil pH to highly acidic levels below 6.0 pH is the excessive application of nitrogen fertilizers. Luckily, you can raise the soil pH of such lawn soils to the appropriate levels by adding wood ash.

Boosts Grass Root Development

One macronutrient that wood ash contains in abundance is potassium, which is known to enhance root development in turf grasses. Through deeper root growth, grasses are more capable of surviving under conditions of prolonged drought, as the extensive roots draw water from deep in the soil.

Boosts Overall Grass Health and Vigor

The potassium in fireplace ash also helps turfgrass to thrive and stay healthy by facilitating carbohydrate synthesis and regulating metabolism. With improved metabolism and higher energy levels, grass becomes more resilient to common turf diseases.

How to apply ash to your lawn

When applying fireplace wood ash as lawn fertilizer, you should factor in various precautions to avoid or lower the chances of grass damage. These include spreading ash only on established turfs, doing a pH test prior to using wood ash, and applying light amounts gently and evenly.

How to apply ash to your lawn

1. Apply wood ash only on lawns

If you’ve just recently seeded or overseeded your lawn, it’s not advisable to use wood ash on it. That’s because the salts in the ash are too strong for the young seedlings to handle and they’ll die. Ideally, the best time to apply wood ash to your lawn is before seeding/overseeding, or after the turf is established and is starting to fill in. At this stage, the grass is developed enough to withstand the ash salts, so long as it’s not excessive.

2. Test the soil pH before applying wood ash

Before spreading wood ash on your lawn, undertake a pH soil test first. Remember, you don’t want to add ash to lawn soil that’s already alkaline, as it’ll raise the alkalinity even further to levels that are dangerous for your turfgrass. The soil chemistry test will let you know whether you need to add wood ash at all, and if so, how much is needed.

3. Apply light amounts of pure wood ash

Also, if you’ll be spreading wood ash directly on your lawn, apply light amounts. High amounts of ash produce lye and salts when it rains or when you irrigate the lawn after applying the wood ash fertilizer. The more the amount of ash, the more the amount of lye and salts, and the higher the potential for turf damage via grass burn.

You can completely avoid the above problem by adding wood ash to your compost first before applying the compost as a lawn fertilizer. Composting wood ash causes the lye and salts to be washed away, making the wood ash safe for grass even when wet.

4. Apply wood ash on calm days

When applying wood ash, ensure gentle application. You don’t want to scatter it into the wind, as this can cause eye irritation. Also, it could be that you have a garden close to your lawn whereby you deliberately lowered the soil pH to acidic to facilitate the vigorous growth of acid-loving plants like blueberries.

In such cases, scattering the fireplace wood ash may cause some of the ash to drift to the garden. And since wood ash raises soil pH, the development and fruit/flower production of the acid-loving plants will be affected.

To prevent wind from carrying away wood ash into your garden, lightly wet up the lawn prior to application. This will ensure that the ash particles stick to the soil and can’t be blown away.

5. Spread the ash evenly

To apply wood ash correctly, gently spread it on the lawn before using a rake to ensure a more even spread and deeper penetration into the soil. An even spread is important since lumped-up piles of ash contain excess salts that when washed into the soil, raise the chances of turf damage in that given section of the lawn.

6. Avoid mixing wood ash with nitrogen fertilizers

While rich in nutrients like potassium and calcium, wood ash doesn’t contain any nitrogen. This usually misleads many homeowners into mixing ash with nitrogen fertilizers. Doing so is detrimental to turf growth and development, as wood ash reacts with ammonium-based nitrogen products and the nitrogen is lost.

The best approach would be to apply the wood ash first to correct potassium deficiencies. Then, after about four weeks or so, when the wood ash alkalinity in the soil has started to diminish, follow up with a slow-release nitrogen fertilizer.

7. Avoid using contaminated wood ash

If the wood you’d burnt in your fireplace was treated by staining or painting, avoid using its ashes as lawn fertilizer. Such wood ash has chemical contaminants from the paints which cause soil pollution when washed into the soil.


  • L. Mark Risse, Professor, and Director, Crop & Soil Sciences, University of Georgia Extension: Best Management Practices for Wood Ash as Agricultural Soil Amendment
  • Hailin Zhang, Oklahoma State University Extension: Fireplace Ashes for Lawn and Garden Use

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